Recently, the applications of photographic light-sensitive materials have been devirsified. For example, in compatibility with miniaturizing of photo taking units, it is known that light-sensitive materials with a thinner support for photographic use are effective. However, in the case of a thinner support for photographic use, so-called stiffness is weakened. Accordingly, there are problems that transportation property and operability in a photo taking unit and developing processes become deteriorated. In order to solve the above-mentioned problems, it is necessary to enhance mechanical strength of a support for photographic use. Especially, the value of elastic module is necessary to be enhanced than that of the conventional support.
Typical plastic film supports currently used are triacetyl cellulose (sometimes abbreviated as TAC) and polyethylene terephthalate (sometimes abbreviated as PET).
A TAC film used for a film in roll mainly has a property to have a high transparency without optical aeolotropicity and also has an excellent property that curling is recovered after being developed. However, since the TAC film has a drawback that the mechanical strength is weak in itself, it cannot reduce the thickness thereof.
On the other hand, a PET film has an excellent mechanical strength and size stability. Therefore, it is used in a sheet form film such as a film for X-ray film use. However, when the PET film is used in a roll film form which is widely used as a photographic light-sensitive material, it is difficult to recover curling after being developed and it is poor in handling property. Accordingly, the range of application is limited.
As a technology to improve curl recovering property of the PET film, a copolymer PET film provided with hydrophilicity by using an aromatic dicarboxyl acid having a metallic sulfonate group as a copolymerization component (see Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 244446/1989). However, when a photographic light-sensitive material is prepared using the polyester film obtained in the above-mentioned manner, photographic emulsion layers are formed on one side of the support. Since elasticity of these emulsion layers in accordance with the change of temperature is larger as compared to that of the support, concave curling occurs on the emulsion layer surface when it is left under low humidity after having been subjected to development. Accordingly, operability after subjected development is reduced.
In order to solve the above-mentioned problems, there are several means for providing anti-curling property such as to laminate polyester layers having different specific viscosities, to heat at different temperatures to the two top and bottom surfaces during vertical stretching or heat setting when a support is manufactured and to permeate the support with an organic solvent such as toluene, phenol or hexane on only one side and evaporate the above-mentioned solvent by heating.
On the other hand, when a film disclosed in Japanese Patent O.P.I. Publication No. 235036/1992 wherein a copolymerization polyester having an aromatic dicarboxylic acid having a metallic sulfonate group and a polyalkylene glycol as the main copolymerization components and a polyester including PET mainly are laminated, adhesive property between the polyester layer and the copolymerization polyester layer is poor. When such films are used at extremely low temperatures, for example, below the freezing point, the polyester layer and the copolymer polyester layer are liable to be separated at their interface.
In order to solve the above-mentioned problems, there exists a technology to use two adjacent polyester layers which are similar in chemical composition or a technology to incorporate the polyester component contained in one layer into the other layer. Thus, the polyester support which is similar in the composition of two adjacent polyester layers is obtained, however, the present inventors have discovered that, when there is a large difference between the composition of the two adjacent polyester layers, sufficient adhesion at a low temperature cannot be obtained.